Periodicity : The properties of elements which change gradually with change in electronic configuration and repeats in regular intervals are called periodic properties and this repetetion is called periodicity.
(a) Atomic size (or) Atomic radius :
In groups : In groups from top to bottom atomic size increases. This is due to the entering of electrons into new subshells each time.
In periods : In periods from left to right (atomic radius) atomic size decreases. This is due to the entering of electrons into same subshell each time.
(b) Ionization energy :
In groups : In groups from top to bottom I.E. decreases this is due to the increase of atomic size in groups.
In Periods : In periods from left to right I.E. increases this is due to the decrease of atomic size in periods.
(c) Electro negativity :
In groups : In groups from top to bottom electron negativity decreases. This is due to the increase of atomic size in groups.
In periods : In periods from left to right electro negavitity increases. This is due to the decrease of atomic size in periods.
